There are already known various constructions of pumped optical fiber lasers, among them such utilizing fully or partially reflective coatings on the respective end faces delimiting the laser resonance cavities in the optical fibers, and such using external mirrors to delimit the laser cavities. Even though these solutions have achieved quite a degree of success and/or acceptance in the laser manufacturing and utilization fields, they still suffer of certain drawbacks that make them hardly suitable or totally unsuitable for certain uses, particularly those where operation in only a single longitudinal mode is desired or mandatory.
With increased use of lasers in communication and sensor applications, there is a pronounced need for laser sources that can be continuously tuned and/or chirped. To achieve this, it was proposed to use intracore Bragg gratings as end reflectors delimiting the laser cavity in the optical waveguide, and to apply strains or temperature variations to such gratings alone, thereby changing their peak reflectivity wavelength. Experience has shown, however, that this results in a situation where the tuning is discontinuous in that the fiber laser, while tuning linearly, will also mode hop between adjacent longitudinal modes, that is, not tune smoothly between such modes. This may be of a particular disadvantage in optical communication in that the mode hopping may introduce undesirable noise into the signal.
In other types of lasers, smooth continuous tuning has been attained by simultaneously varying a wavelength dependent feedback of the resonator (i.e. refraction grating or etalon) and the optical cavity length. In most types of lasers, however, this is a very difficult proposition and the solution is correspondingly complex and costly, requiring closely toleranced optics mounts and controls.
Accordingly, it is a general object of the present invention to avoid the disadvantages of the prior art.
More particularly, it is an object of the present invention to provide a pumped optical fiber laser arrangement which does not possess the disadvantages of the known arrangements of this kind.
Still another object of the present invention is so to develop the laser arrangement of the type here under consideration as to be able to continuously tune the same while avoiding longitudinal mode hopping.
A concomitant object of the present invention is to design the optical fiber laser arrangement of the above type in such a manner as to be relatively simple in construction, inexpensive to manufacture, easy to use, and yet reliable in operation.